Apple let down iPhone watchers and owners when it announced in June that iPhone 3.0 software would support MMS but implied that AT&T would not yet allow it. The service launch was delayed several times, with exclusive carrier AT&T citing the need to make sure its network was ready. The feature will finally become generally available on AT&T iPhones on Friday when iTunes delivers a carrier settings update for the wildly popular phone. The carrier has said it expects “record volumes” of MMS traffic after the launch. MMS lets people send pictures, audio recordings, video clips or contact information along with an SMS (Short Message Service) message.

However, the service in question has been out for years on other handsets and hasn’t exactly taken the mobile world by storm. In 2008, MMS made up just 2.5 percent of all messages sent from phones worldwide, meaning about 97.5 percent were SMS text messages, according to ABI Research. ABI expects the MMS share to grow to just 4.5 percent by 2014.

Given the amount of data that iPhone fans are already using on AT&T's network, for Web browsing, video, e-mail and social networking, it would take quite a popularity breakthrough for MMS to drag down the infrastructure through sheer traffic, analysts said. However, the carrier’s fears in one respect may have been justified, said ABI analyst Dan Shey.

Several factors have dampened the popularity of MMS, according to analysts and industry observers. A big one is that the messages still don’t always get through.

“Interoperability between carriers has always been an issue, and that’s why MMS usage hasn't really taken off,” Shey said. Delivering multimedia content from one phone and one network to another can be complicated with photos and gets even more involved when it comes to video, with large file sizes and multiple available formats, he said. What’s attached in an MMS, 98 percent of the time, is just a picture, he said.

Another problem has been the complicated user interfaces on some phones and networks, which at times have forced senders to go through several steps to attach their content and recipients to go to a link within an SMS and provide a password along the way. The iPhone streamlines this process for iPhone users but not necessarily for the recipients of their messages.

The economics of MMS may not be attractive for either users or service providers. Even though each message uses a lot more network capacity than an SMS, which is limited to 160 characters of text, they typically count the same as an SMS against a bundled plan, Shey said. As a result, carriers haven’t had an incentive to market the capability, he said.

And users of advanced phones now have alternatives to being charged for sharing content with their friends. For example, it’s possible to post a photo to a Facebook page directly through Facebook’s iPhone application.

Carriers will eventually figure out a way to monetize user sharing of content, but it probably won’t be through MMS, said Mark Jacobstein, CEO of iSkoot, at the Mobilize conference earlier this month in San Francisco. Jacobstein is a serial entrepreneur in the mobile data world whose current company develops a variety of phone software. “The problem is not demand but implementation,” he said.

The increase in MMS traffic from iPhone users isn’t likely to put a much greater strain on AT&T’s network, said In-Stat infrastructure analyst Allen Nogee. The carrier’s current woes stem from having to deploy new base stations for 3G while selling a hugely popular handset that subscribers love to use for data, he said. Most customers won’t just send one big MMS after another and overload the network, Nogee said.

However, AT&T may have had good reason to make sure its infrastructure was ready for MMS, ABI's Shey said. Even if the new feature doesn’t swallow huge amounts of overall capacity, all those messages eventually need to be separated out and sent through an exchange point called an MMSC (MMS service center). AT&T’s engineers may have set up that infrastructure for a smaller number of messages and then faced the prospect of MMS becoming possible on all iPhones.

If they learned anything from the experience of watching data traffic grow exponentially after the iPhone itself hit the market, they may have wanted to beef up the MMS portion of their system before the new feature hit all those phones, Shey said.

“All operators are just fanatic about ensuring that their network is not overutilized,” Shey said. “I’m sure the network folks got involved and said, ‘We’d better test this.’”